A hard-disk drive (HDD) is a non-volatile storage device that is housed in a protective enclosure and stores digitally encoded data on one or more circular disks having magnetic surfaces (a disk may also be referred to as a platter). When an HDD is in operation, each magnetic-recording disk is rapidly rotated by a spindle system. Data is read from and written to a magnetic-recording disk using a read/write head which is positioned over a specific location of a disk by an actuator.
In order to assist in the positioning of the read/write head, a HDD may undergo a self servo write process in which the HDD writes servo information onto the disk. When read back, servo information provides a continuous update on the location of the read/write head. A low density gas, such as helium, may be introduced into the interior of the HDD when the HDD performs a self servo write process to reduce excitation of the disk, actuator, and head.
A read/write head uses a magnetic field to read data from and write data to the surface of a magnetic-recording disk. As a magnetic dipole field decreases rapidly with distance from a magnetic pole, the distance between a read/write head and the surface of a magnetic-recording disk must be tightly controlled. An actuator relies on suspension's force on the read/write head to provide the proper distance between the read/write head and the surface of the magnetic-recording disk while the magnetic-recording disk rotates. A read/write head therefore is said to “fly” over the surface of the magnetic-recording disk. When the magnetic-recording disk stops spinning, a read/write head must either “land” or be pulled away onto a mechanical landing ramp from the disk surface.
To prevent damage to the sensitive interior components of the HDD by the introduction of harmful airborne particles, the HDD is encased in a protective enclosure. The protective enclosure is designed to be airtight, with the exception of intentional openings in the enclosure that are protected by particle filters. A typical protective enclosure is formed using two components called a cover and a base. The cover and the base may be sealed with the assistance of a cover gasket.
A popular type of low cost cover gasket is cured with a short exposure to ultra violet (UV) light. Under some conditions, this can result in a surface morphology that allows the rapid diffusion of gas therethrough while nevertheless appearing to hold gas using a conventional pressure test. Currently, this condition is only detected when the HDD fails a key test after the self servo write process. While it is possible to measure gas leakage through the protective enclosure of the HDD after the HDD has been assembled, if the source of the leak is a defective cover, then many drives will have already been built before the problem is detected. In addition, large stocks of problematic covers may already be part of assembly plant stock.